(meth)acrylic-modified siloxane compounds

This non-provisional application claims priority under 35 U.S.C. §119(a) on Patent Application No. 2008-115740 filed in Japan on Apr. 25, 2008, the entire contents of which are hereby incorporated by reference.

This invention relates to (meth)acrylic-modified siloxane compounds which are highly compatible with and added to various heat or photo-curable compositions such as film-forming compositions and resin compositions, which cure into products exhibiting intrinsic properties of siloxane such as water repellent, antifouling and lubricating properties. It also relates to curable compositions comprising the same.

In general, organopolysiloxanes are admixed in various compositions such as coating and resinous compositions since they are effective in imparting or enhancing some properties like antifoaming, water repellent, parting, antifouling, lubricating, heat resistant, freeze resistant, electrically insulating, and flame retardant properties. Particularly, polyether-modified siloxanes in the form of hydrophobic polysiloxane combined with hydrophilic polyether are further effective in promoting emulsification and dispersion of resin components in coating compositions. As for (meth)acrylic-modified siloxanes in the form of polysiloxane having heat or photo-curable (meth)acrylic groups bonded thereto, cured compositions exhibit persistent polysiloxane properties because the siloxane is incorporated in the cured compositions via chemical bonds. Thus polyether-modified siloxanes and (meth)acrylic-modified siloxanes are useful in a variety of applications including coating, ink and resin compositions as coating additives (e.g., leveling, antiblocking, dispersing and antifoaming agents), surface treating agents for imparting water repellency, heat stability, lubricity and flexibility, or resin modifiers.

However, some polyether-modified siloxanes having a high content of hydrophilic polyether group are not dissolved in hydrophobic coating compositions and are insufficient to manifest and maintain antifouling and other functions. Even in the case where polyether-modified siloxane is fully compatible with a resinous component in a coating or resinous composition prior to curing, when the composition is cured, the resinous component can become less compatible with the polyether-modified siloxane due to a change of water content during curing or a molecular weight buildup with the progress of curing reaction. Then such phenomena as surface delamination, weak adhesion and color shading can occur in the cured product.

On the other hand, (meth)acrylic-modified siloxanes are less soluble in coating compositions, separable therefrom, and less reactive with other curable components. The coating compositions become less antifoaming or dispersible and lack storage stability.

A composition comprising a siloxane compound having both polyether and (meth)acrylic groups is reported as overcoming the drawbacks of the polyether-modified siloxane and (meth)acrylic siloxane.

Namely, JP 3963755 describes a polyurethane composition comprising a silicone modified with both polyether and methacrylic carbonyloxy groups as an internal parting agent. However, when the silicone has methacrylic groups at both ends of a siloxane link, it rather functions as a crosslinking agent and is unlikely to exhibit parting, antifouling and lubricating properties.

JP-A 2004-149592 discloses a resin composition (for decorative boards) comprising a polyether-modified silicone having an acryloxy or methacryloxy group and a polyoxyalkylene group. However, only siloxane compounds having (meth)acrylic groups on side chains and both ends are shown in Examples. They also function as a crosslinking agent and are unlikely to exhibit siloxane properties. When a number of (meth)acrylic groups are included within the molecule, siloxane compounds can become gelled, making it difficult to control physical properties of the cured composition.

Although curable compositions comprising a modified silicone having both (meth)acrylic and polyether groups bonded thereto are known in the art, compounds capable of exhibiting siloxane properties to a full extent and compositions comprising the same are not yet available.

An object of the invention is to provide (meth)acrylic-modified siloxane compounds which are highly compatible with and added to various heat or photo-curable compositions such as film-forming compositions and resin compositions, which cure into products exhibiting water repellent, antifouling, lubricating and other intrinsic properties of siloxane to a full extent; and curable compositions comprising the same.

The inventors have found that a (meth)acrylic-modified siloxane compound is obtained by modifying a siloxane compound at one end with at least one (meth)acrylic group. A spacer intervenes between the siloxane and the (meth)acrylic group and is a straight chain having at least three ether bonds or a branched structure having at least one ether bond. This (meth)acrylic-modified siloxane compound is highly compatible with a heat or photo-curable composition such as a film-forming composition or resin composition. The composition having the (meth)acrylic-modified siloxane compound added thereto, when cured, exhibits water repellent, antifouling, lubricating and other intrinsic properties of siloxane to a full extent.

Accordingly, the invention in one aspect provides a siloxane compound having one end modified with at least one (meth)acrylic group via a spacer, the spacer being a straight chain having at least three ether bonds or a branched structure having at least one ether bond.

Typically the (meth)acrylic-modified siloxane compound has the structural formula (1):

wherein R¹ is each independently a monovalent C₁-C₃₀ organic group, R² is C₂-C₆ oxyalkylene, R³ is an organic group of straight or branched structure which is terminated with one to three (meth)acrylic groups and may further have a spacer, i has a value from 1 to 500, and j has a value of 2 to 60 in the case of straight structure or 0 to 60 in the case of branched structure.

In a preferred embodiment, the (meth)acrylic-modified siloxane compound has the structural formula (2) or (3).